The objective of the proposed work is to evaluate quantitatively two important aspects of electromagnetic irradiation of biological systems. One aspect involves the thermal response of humans to whole body irradiation. This part of the study will be conducted by developing a comprehensive mathematical model for computing specific absorption rates and transient-state temperature profiles for irradiation under various conditions. Factors which will be evaluated using this model include the following: frequency and polarization of the incident field, subject's size, exercise, clothing, and environmental conditions. The other aspect of the study involves an experimental investigation of changes in the permeability of cellular and endothelial membranes owing to microwave irradiation. New and innovative experimental techniques of stopped-flow spectrophotometry, computerized microscopic densitometry, and digital velocity correlation will be applied to the analysis of transient and steady state alterations of tissue transport function. Specific studies will be conducted to characterize the biological response to microwave irradiation according to: (1) the permeability of human erythrocytes and cultured cells to water and solutes, (2) the extravasation and interstitial diffusion of plasma macromolecules in the microvascular bed, and (3) the in vivo velocity of blood flow in the microcirculation.